1. Technical Field
The present invention relates to a method of driving an electrophoretic display provided with dispersion system including electrophoretic particles.
2. Relate Art
Dispersing micro particles having positive or negative electric charges into a liquid and applying electrical field to them from outside makes these micro particles migrate by a coulomb power. This phenomena is called as electrophoretic migration and a display using the electrophoretic migration is well known as an electrophoretic display (EPD.) Such electrophoretic display is better suited for an electronic paper. In particular, an active matrix type display in which pixel electrodes are arranged in a matrix is under development. JA2002-116733 is an example of a related art regarding such development.
An active matrix type electrophoretic display (AMEPD) is provided with a plurality of scanning lines and signal lines, which are orthogonally arranged each other. An electrophoretic element, is provided at the cross section between a scanning line and a signal line, forming a pixel. Each of pixels includes a switching transistor and a pixel electrode. One of pixels arranged in a matrix is sequentially selected by a switching transistor and a predetermined image is introduced into each of pixel, forming a piece of an image. An example of a driving method for image displaying is explained referring to FIG. 7. An AMEPD comprises an active substrate, an opposing substrate and a dispersion system between these substrates. The active substrate includes scanning lines, signal lines and pixels (pixel electrodes and switching transistors) formed thereon. The opposite substrate has a common electrode. The dispersion system includes an electrophoretic element (an electrophoretic material.) An voltage Vcom which is common for all pixel electrodes is applied to the common electrode and a predetermined image signal is applied to each of pixel electrodes. A period for forming a piece of an image in a AMEPD is defined as a period for forming an image in the invention. In the conventional, the period for forming an image includes a reset period and a period for introducing an image signal. The reset period is a period for erasing a previous image. On the other hand, the period for introducing an image signal corresponds to a period for forming a new image in a AMEPD. In a AMEPD comprising M numbers of scanning lines and N numbers of image signal lines which are arranged in a matrix, one of the scanning lines is sequentially selected and, then an image signal is applied to the N numbers of pixels connected to the selected scanning line during this selected period. A period when one scanning line is selected, is called as a horizontal scanning period and a period when all scanning lines are selected (M times of horizontal scanning periods), is generally called as a frame period. In the conventional technology, the period for introducing an image signal included the frame period and M times of the horizontal scanning period (a vertical scanning period) and the reset period, forming a piece of an image in a MEPD.
In an electrophoretic display, micro particles physically migrate in a dispersion medium, changing spatial distribution of micro particles between a pair of substrates, thus changing displaying. A period when micro particles migrate in a dispersion medium at the time of applying voltage corresponds the response time of an electrophoretic display. This time is several milliseconds at the shortest, generally several hundred milliseconds. Namely, time for changing an image is about several hundred milliseconds. Hence, a horizontal scanning period was from several tens milliseconds to several hundred milliseconds in the past. The conventional AMEPD having small numbers of pixels and low resolution used this simple driving method.
However, if a new AMEPD having increased numbers of pixels and high resolution is manufactured, the numbers of scanning lines (M) are increased several hundred numbers and a period for forming an image (1 frame period) becomes several seconds or several tens seconds. Then it becomes a problem that the state of changing an image corresponding to selecting a scanning line is recognized by a viewer and it is uneasy to see changing display.